The present invention generally relates to a system and method for coating substrates. More specifically, the invention relates to a plasma coating system and method whereby the introduction of reagents is controlled to enhance the coating formed on the substrate and conserve the amount of reagents used in forming the coating.
Generally, plasma coating systems, to which the present invention is applicable, include various stations or zones connected in sequence and through which substrates are moved in a continuous series. These stations may include a load lock, a heating station, one or more coating stations and an exit lock. In the coating station(s) is one or more plasma sources, such as an expanding thermal plasma (ETP) source, and an associated reagent manifold(s) for injecting the reagent. During the coating process, the substrates are moved past the plasma source(s) as a coating reagent(s) is injected into the plasma jet issuing from the plasma source. As the substrates are moved through the resulting plasma plume, the coating is deposited on the surfaces of the substrates.
Typically, coating stations continuously supply reagents during the coating process. This generally results in overspray, excessive coating build-up and excessive use and wastage of the reagents.
Moreover, in certain systems, plasma sources are located on opposing sides of the coating station to enable the coating of both sides of the substrate. In such a coating station, the balancing of the opposing plasma plumes, so as to minimize or prevent overspray, is difficult to achieve and generally cannot be consistently maintained during production runs. As a result, opposing plasma plumes may mix when the plumes are not fully intercepted by a substrate. This may further result in specific precursors condensing on an unintended side of the substrate, for example, on the side of the substrate that does not directly oppose the plasma source that generated the plasma plume carrying that specific precursor.